The lithium ion secondary battery has been widely used as, for example, the power source of a notebook PC, a video camera, a cellular phone, and an electric vehicle. As this lithium ion secondary battery, one having a configuration in which the circumference of the battery body portion (body portion containing an anode, a cathode, and an electrolyte) is surrounded with a case has been used. As the case material (packaging material), one having a configuration in which an outer layer containing a heat-resistant resin film, an aluminum foil layer, and an inner layer containing a thermoplastic resin film are bonded and integrated in this order is known, for example.
In the lithium ion secondary battery and the like, gas is likely to be generated in the battery body portion when the battery is overcharged or the temperature excessively rises, and therefore the gas is gradually accumulated in the internal space covered with the packaging material, so that the internal pressure in the packaging material rises in some cases. When the internal pressure rise becomes high, there is a concern that the packaging material is burst, so that the contents inside the battery are scattered. Therefore, techniques of preventing such burst of the packaging material have been proposed.
For example, Patent Document 1 describes an electricity accumulation device with an burst-proof function having an electrode laminate in which an anode and a cathode molded into a sheet shape are laminated through a separator, in which the electrode laminate is accommodated in a container formed with a metal laminate film with an electrolytic solution and the container is hermetically sealed with a heat sealing portion obtained by thermally bonding the metal laminate film in a belt shape along the outer periphery of the container, and the device having a perforating device having an edge support attached and fixed in a state where the portion of the outer periphery of the container is sandwiched and an edge member supported by the edge support and disposed on the side of the center portion relative to the heat sealing portion in the container, in which the edge support moves in the outer peripheral direction of the container by being pushed out by the container which is expanded and deformed when gas is generated and the edge member moves with the edge support to thereby tear the container.
Moreover, Patent Document 2 describes an electricity accumulation element having an electricity accumulation element body impregnated with an electrolytic solution, a packaging body which seals the electricity accumulation element body, a first gas discharge mechanism portion provided inside the packaging body, and a second gas discharge mechanism portion provided on the outside of the packaging body, in which gas from an internal space of the packaging body where the electricity accumulation element body is present successively passes through each of the gas discharge mechanism portions, and thus the discharge of the gas from the internal space to the outer space is permitted, and the element having a pressure adjustment device which prevents the entry of the gas from the outer space into the internal space by each of the gas discharge mechanism portions, in which each of the gas discharge mechanism portions is provided with a buffer space individually divided by each of the gas discharge mechanism portions.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-156404
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2012-156489